Essential hypertension (HTN) is a major health problem, afflicting 30% of the population and predisposing to serious diseases affecting the brain, heart and kidneys. There is compelling evidence that essential HTN is characterized by neurohumoral dysfunction, and inappropriate angiotensin II (AngII) signaling in the central nervous system (CNS) is a primary culprit. The subfornical organ (SFO), a forebrain structure that lacks a blood-brain-barrier and is considered a key gateway to the CNS for circulating factors, is strongly implicated in AngII-dependent HTN. In previous cycles of this grant, we have shown that AngII (type 1 receptor, AT1R)- induced reactive oxygen species (ROS) signaling in the SFO mediates slow-pressor AngII HTN, a chronic mouse model that recapitulates key features of essential HTN. However, our understanding of how AngII- induced ROS formation in the SFO translates into powerful effects on neural pathways controlling blood pressure is still incomplete. Recently, endoplasmic reticulum (ER) stress has emerged as a major redox- associated mechanism in a number of cardiovascular and metabolic diseases; its role in HTN, however, is not known. AngII is now directly linked to ER stress in several cardiovascular cell types, and ER stress in the CNS leads to long-term changes in neural function through molecular mechanisms known to be involved in brain AngII-dependent HTN. During the past year, we have obtained exciting preliminary data showing links between AngII, ROS and ER stress in cultured neurons and in the SFO in vivo, along with evidence that chemical manipulation of ER stress in the CNS has significant effects on blood pressure. Based on these findings, we propose to test the overall hypothesis that ER stress in the SFO provides an important link between AngII, ROS and CNS alterations that lead to HTN in the AngII slow-pressor mouse model. Aim 1 will utilize molecular, immunocytochemical and ultrastructural analyses to test the hypothesis that AngII induces AT1R- dependent ER stress in the SFO in vivo. Aim 2 will test the hypothesis that the coupling of ER stress and oxidant stress is critical in slow-pressor AngII-mediated effects in the SFO. This will be accomplished through a combination of viral delivery of ROS scavengers, a genetic ER stress inhibitor and oxidative fluoroprobes for ROS measurements in the SFO in situ. Aim 3 will utilize SFO-targeted genetic manipulations of ER capacity combined with integrative cardiovascular physiology to test the hypothesis that ER stress in the SFO is a causal factor in slow-pressor AngII HTN and related neurohumoral sequelae. A notable strength of the project is the involvement of investigators with complementary expertise in central neural cardiovascular regulation and HTN (Davisson, Mark), ER stress biology (Kaufman, Qi), redox biology (Davisson, Kaufman) and neuroanatomy of CNS CV circuits (Pickel, Pierce). This project, which addresses a highly novel topic in HTN research, has the potential to fundamentally advance understanding of basic mechanisms linking the CNS with HTN, which could provide clues into novel treatments. The project also has the potential to forge new trails in HTN research.